GMM

Hi guys,

Built a 28h wheel set a while ago (Ultegra w/ Swiss rims) but am finding the rear too flexy and the drive-side spoke tensions are already at the higher-end.
Talked with a DT rep and he recommends going with a 3x rather then 2x to control the flex.

The question is; would changing the spoke angle (from 2x to 3x) compromise the hubs flange in any way since the spokes have already settled-in at 2x angles?

I'm sure it'll be fine, but thought I'd double-check with you guys.

Thanks

Sixty Fiver

You should be fine... going from 2x to 3 x and maintaining the lacing pattern at the hub will place the new spokes offset from where the 2x spokes were laying.

The risk here is that lacing up a wheel with a different spoke pattern can cause the new spokes to cross the old lacing where is may have scored the hub flange.

If you were re-lacing 2x you would also want to maintain the spoke positions at the hub flange.

hueyhoolihan

are you asking this question thinking that the 3x will possibly result in a laterally stiffer wheel?

BTW, there is a thread on this forum that addresses lateral stability in wheel building, and although i haven't checked in recently, i suspect it may have devolved into a ...er... dispute.

mrrabbit 

And I have to add...are sure it's not rear triangle flex rather than rear wheel flex that's the problem?

=8-)

fietsbob

it's a 28 hole Rear, and you wish for it to be More laterally stiff?
How about just building with 4~8 more spokes in the new wheel?

you may have gone too few for the stresses the bike actually sees.

save the other for the trainer stand,
since there the load is mostly transferred to the trainer base.

ultraman6970

Well IMO 3x will do better than 2x, but u have to consider that u will need new spokes, the new ones will, besides that pretty much is the same thing for the hub, unless the holes are really bad and used the hub shouldn't be a problem at all, and even if the spoke holes are in bad shape u can add washers and problem solved.

Soil_Sampler

what spokes? Revos?
what swiss rim? 465?585?
how much do you weigh?

GMM

Ultegra Hubs, R450 rims, Competition butted spokes, 2x L+R, properly dished.

"Flexy" = the pull-spokes are pulling the push-spokes outward into the RD’s cage when climbing even though spoke tension is correct. Yes, RD is properly ajusted.

I have no such issue with a 32 3x wheel built with the same Competition spokes.
AND
I have no such issue with a 24 2x wheel built with Champion spokes either.

Remember guys; 32h rear wheels only add 2 more pull spokes, or more realistically, 1 driveside pull spoke.

Thinking it’s a 2x issue rather then overall spoke count issue.

FBinNY 

FWIW, you might want to reconsider the advice that a 3x pattern will be stiffer than a 2x. Though the difference will probably be so small as to be academic, I suspect the opposite is true.

There are two reasons that 2x would tend to be stiffer than 3x.

1- Wheels get stiffer when the bracing angle widens, and reducing cross widens the bracing angle.
2- Shortening the spokes (all other things staying equal) makes them stiffer. Reducing cross shortens spokes, so makes the wheel stiffer.

Remember the differences are very small, not feelable (except by placebo effect) and barely measurable with instruments, so rebuilding changing only the number of crosses won't give you the solution you're looking for, even if you went in the right direction.

Before you waste the time and effort on a rebuild, try to find out the real problem. If it actually is wheel flex maybe it was just a bad build. Otherwise, it could be a poor tire/rim combination, frame flex, of hub play.

One final note. The only way to measurably stiffen a wheel is to use more steel, either thicker spokes, or more spokes or both. To complement the added steel you may also need to add more rim, otherwise you could end up with spokes too strong for the rim.

Kimmo

It's torsional stiffness the OP's complaining about.

He seems to have a pretty good indicator of it not being up to scratch, too. The leading spokes hitting the derailleur are a side-effect of torsional flex. If we believe the OP's successfully narrowed it down to spoke tension.

IMO there's likely to be at least a small improvement going to 3x, for the same reason it's not smart to lace a rear radially.

You could also try using beefier trailing spokes.

mrrabbit 

1. Get a second opinion on whether the tension is right or not - for all you know the tensionmeter used previously was out of calibration. Tensionmeters out of calibration will read artificially high.

2. Have you verified up close the spokes are doing as you said? In stand, wheel braced by Mr. Charles, Mr. Arnold standing on a pedal...Mr. PeeWee watching the rear...

(I know, that sounded gross...)

I'm leaning toward FBinNY...crossing changes for same spokes and hub results in very minor changes...it's going all radial with heads in for the same hub and spokes that makes a noticeable difference.

If these are 14/15/14 spokes, that's plenty already for a light weight road wheel - unless you are a really big dude...

=8-)

FBinNY 

Sorry, I started writing my post before the OP clarified his problem with his second post.

If torsional stress is moving the point of cross outboard the solution isn't to go from 2x to 3x which will only yield a marginal improvement at best.

The solution is to mirror the pattern and build the way Jobst Brandt does with the trailing spokes coming off the inside of the flange and passing to the outside at the cross. Mr. Brandt is a firm advocate of this pattern as it moves the point of cross inward under torsional load.

OTOH, I build the way the OP did, with trailing spokes to the outside of the hub, and in 40 years have never had an issue with the point of cross moving far enough to matter, and there are some damn steep hills here. I don't believe that there's enough change in torsion load on a properly tensioned wheel to move the cross in or out a significant distance.

I repeat my suggestion that the OP diagnose the real cause of his problem, which in all likelihood isn't the wheel deflecting as much as it is that the RD cage is too close the the spoke plane, possibly because of a slightly bent hanger. A tiny tweak of the hanger will increase the RD cage clearance solving the problem without changing RD performance.

It's also possible that lateral flex is a contributing factor if the OP has a climbing style that rocks the bike for power.

While I agree that increase the cross will lower torsional stress, it isn't a big difference. The OP can calculate a percentage improvement by measuring the distance form the center to the line of the spoke (at right angles) and comparing that of 2x and 3x.

So the OP has choices,

1- get marginal improvement by building the same way with 3x
2- stiffen the wheel with heavier spokes on the right flange, again probably not enough to make much difference
3- solving the problem (if cross deflection is the problem) by lacing trailing spoke inside the flange
4- solving the problem, by increasing the RD cage to wheel distance, which IMO is way too close if wheel deflection is enough to make contact in the first place.

mrrabbit 

4- solving the problem, by increasing the RD cage to wheel distance, which IMO is way too close if wheel deflection is enough to make contact in the first place.



...and get tension second opinion. Even outside trailing shouldn't be a problem...as FBinNY noted...

=8-)

GMM

<ANOTHER UPDATE>

Tightened all spokes 1/2 turn, everything fine now - no rubbing, no flex, wheel's nice and tight.